Carboxymethylation of cellulose using reactive extrusion

Carboxymethyl cellulose was prepared using a continuous, reduced solvent, reactive extrusion process with a short reaction time. The effects of the amounts of NaOH (30 g, 40 g and 50 g), water:ethanol ratio (100%, 70%, 50%, 30% and 10% H2O) and their interactions on the physical, chemical and morphological properties of carboxymethyl cellulose were studied. Experiments were conducted using to a 5 x 3 blocked factorial design. X-ray diffraction analyses revealed higher degrees of crystallinity and fractions of cellulose-II crystalline structure when 100% H2O was used as compared to that for 70%, 50%, 30% and 10% H2O and a commercially available brand of carboxymethyl cellulose, AQUASORB A500. Statistical analysis revealed a significant interaction between the effects of NaOH and H2O on the degrees of substitutions. The degrees of substitutions decreased with increasing amounts of NaOH and tended to increase with increasing alcohol concentrations. Liquid uptake measurements revealed that the extent of saline uptake, measured at intervals of 1 min, 5 min and 10 min, by carboxymethyl cellulose prepared with 100% H2O, especially when 40 g and 50 g NaOH was used, was higher than that for 70%, 50%, 30% and 10% H2O and AQUASORB A500. This may have been because of the higher crystallinity in carboxymethyl cellulose prepared with 100% H2O. Carboxymethyl cellulose prepared with 70% H2O and 30 g and 50 g NaOH had the highest saline absorption, using the soak method, before and after centrifugation, respectively. Scanning electron microscopy for carboxymethyl cellulose prepared with 100% and 10% H2O, through images at 120X magnification, revealed fibers 100 mu to >800 mu in length and 0.8-3.3 mu in breadth. Some non fibrous particles, 0.8-6.7 mu in dimensions, also were observed for 100% H2O. Images at 900x magnification revealed partially damaged fiber surfaces. (C) 2011 Elsevier Ltd. All rights reserved.